The coating of a substrate with an ink or paint or other similar medium having alignable particles or flakes therein to form an image exhibiting optically-illusive effects is known. Many surfaces painted or printed with flat platelet-like particles show higher reflectance and brighter colors than surfaces coated with a paint or ink containing conventional pigments. Substrates painted or printed with color-shifting flaked pigments show change of color when viewed at different angles. Flaked pigments may contain a material that is magnetically sensitive, so as to be alignable or orientable in an applied magnetic field. Such particles can be manufactured from a combination of magnetic and non-magnetic materials and mixed with a paint or ink vehicle in the production of magnetic paints or inks. A feature of these products is the ability of the flakes to become oriented along the lines of an applied field inside of the layer of liquid paint or ink while substantially remaining in this position after drying or curing of the paint or ink vehicle. Relative orientation of the flake and its major dimension in respect to the coated surface determines the level of reflectance or its direction and, or may determine the chroma of the paint or ink. Alternatively, dielectric material may be alignable in an electric field.
Alignment of magnetic particles along lines of an applied magnetic field has been known for centuries and is described in basic physics textbooks. Such a description is found in a book by Halliday, Resnick, Walker, entitled, Fundamentals of physics. Sixth Edition, p. 662. It is also known to align dielectric particles in an electric field, and this form alignment is applicable to this invention.
The patents hereafter referred to are incorporated herein by reference for all purposes.
U.S. Pat. No. 3,853,676 in the name of Graves et al. describes painting of a substrate with a film comprising film-forming material and magnetically orientable pigment that is oriented in curved configurations and located in close proximity to the film, and that can be seen by the naked eye to provide awareness to the viewer of the location of the film.
U.S. Pat. No. 5,079,058 by Tomiyama discloses a patterned film forming a laminated sheet comprising a multi-layer construction prepared by successively laminating a release sheet layer, a pressure-sensitive adhesive layer, a base sheet layer, and a patterned film layer, or further laminating a pigmented print layer. The patterned film layer is prepared by a process which comprises coating a fluid coating composition containing a powdery magnetic material on one side of the base sheet layer to form a fluid film, and acting a magnetic force on the powdery magnetic material contained in the fluid film, in a fluid state, to form a pattern.
U.S. Pat. No. 5,364,689 in the name of Kashiwagi discloses a method and an apparatus for producing of a product having a magnetically formed pattern. The magnetically formed pattern becomes visible on the surface of the painted product as the light rays incident on the paint layer are reflected or absorbed differently by magnetic particles arranged in a shape corresponding to desired pattern. More particularly, Kashiwagi describes how various patterns, caused by magnetic alignment of nickel flakes, can be formed on the surface of a wheel cover.
U.S. Pat. No. 6,808,806 by Phillips in the name of Flex Products Inc., discloses methods and devices for producing images on coated articles. The methods generally include applying a layer of magnetizable pigment coating in liquid form on a substrate, with the magnetizable pigment coating containing a plurality of magnetic non-spherical particles or flakes. A magnetic field is subsequently applied to selected regions of the pigment coating while the coating is in liquid form, with the magnetic field altering the orientation of selected magnetic particles or flakes. Finally, the pigment coating is solidified, affixing the reoriented particles or flakes in a non-parallel position to the surface of the pigment coating to produce an image such as a three dimensional-like image on the surface of the coating. The pigment coating can contain various interference or non-interference magnetic particles or flakes, such as magnetic color shifting pigments.
U.S. Pat. No. 6,103,361 reveals patterned substrates useful in producing decorative cookware formed by coating a base with a mixture of fluoropolymer and magnetic flakes that magnetically induce an image in the polymer coating composition.
A common feature of the above-mentioned prior art references is a formation of one or more patterns in a painted or printed layer. Typically such patterns include indicia such as symbols, shapes, signs, or letters; and these patterns replicate the shape of a magnetic field often located beneath the substrate and are formed by shadowing contour lines appearing in the layer of paint or ink resulting in particular alignments of magnetic flakes. The desired pattern becomes visible on the surface of the painted product as the light rays incident on the paint layer are reflected or absorbed differently by the sub-group of magnetic non-spherical particles.
Although these prior art references provide some useful and interesting optical effects, there is a need for patterns which have a greater degree of optical illusivity, and which are more difficult to counterfeit. United States patent application number 20050106367, filed Dec. 22, 2004 in the name of Raksha et al. entitled Method and Apparatus for Orienting Magnetic Flakes describes several interesting embodiments which provide optical illusivity, such as a “flip-flop” which may serve as the basis of particular embodiments of this invention. Notwithstanding, there is need to provide different patterns on a single substrate wherein an image in the form or text or a logo, or identifiable feature is printed upon a substrate and wherein a coating of aligned flakes is disposed thereover rendering the image as a latent image that is highly visible when viewing at a first angle and barely visible or not visible at all when viewing the image from another angle.
In the past, attempts to make a hidden image in a security printing have been disclosed, for example in U.S. Pat. Nos. 3,640,009, 4,310,180, and 4,668,597.
A printed hidden image is described at the web site of Austria Card (a subsidiary of the Austrian Central Bank). Related information can be found at:
http://www.austriacard.at/main/EN/Products/Indus-tryAndGoverment/SecuritFeatures/index.html. The device described is produced by means of a halftone displacement of the hidden image. The printed hidden image is only visible with a special decoding lens.
Latent Filter Image (LFI®)_is manufactured by TRUB (http://www.trueb.ch/en/products/national/rohkarte.php). The LFI® is like a hidden image which has an integrated decoding filter. Tilting the card displays an inverted image.
Although this printed hidden image is interesting and appears to perform its intended function, it is quite complex and costly to produce and requires registration of a filter with a region supporting the printed hidden image.
It is an object of this invention to form a security device that has a latent image thereon that can be detected or seen at certain viewing angles and which is difficult to see at other angles. Complex instructions are not required to see the latent image. One only has to tilt the image from one direction to another to see the image appear or essentially disappear.